Bump cyclops-infobook-html to 6.1.3

Replaces the fixed background-size on body with a min-height, so the
background gradient covers short pages without repeating on long ones.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DxKmvJ8sEksnwQn1pMRwEE

Author: claude

package-lock.json

@@ -45,7 +45,7 @@
     "generate:compress": "compress-icons output"
   },
   "dependencies": {
-    "cyclops-infobook-html": "^6.1.2",
+    "cyclops-infobook-html": "^6.1.3",
     "pug": "^2.0.4"
   }
 }